10
SAND TEMPER IN PREHISTORIC POTSHERDS
FROM THE TO'AGA SITE
W. R. D cKINSON
TWENTY-NI
RETATIVE sherds selected by
T. L. Hunt from the collection of artifacts
excavated at the To'aga site near the south coast of
Ofu Island in the Manu'a Group of American Samoa
were examined pergraically in thin section. As
there is no current rason to suspect that any of the
To'aga ceramic ware was made elsewhere, the
purpose of the study was to provide baseline information about Manu'a temper sands. All the sherds
examined contain volcanic sand as temper, aithough
this basaltic detritus is mixed with calcareous grains
derived from reef sources in some of the sherds. As
would be predicted for Manu'a and other parts of
Samoa, the volcanic sand is typical of the oceanic
basalt tempers common to intra-oceanic Pacific
archipelagoes (Dickinson and Shutler 1968, 1971,
1979). Several variants of temper sand are present in
different sets of sherds, and available information is
inadequate to pinpoint their
ive sources. All
could p ly have been collected on Ofu or nearby
Olosega Island, but derivation of some from Ta'u in
Manu'a or even elsewhere in Samoa is not precluded
by the petrgric data. Their petrologic compatibility with Samoan lavas, however, and their overall
resemblance to the spectrum of basaltic tempera
studied to date from Samoa, makes importation from
outside Samoa quite unlikely. As none of the temper
variants are identical to tempers known from Tutuila
or Upolu, all are regarded provisionally as indigenous To'aga temper, with the proviso that petrographic evidence alone cannot indicate how far
afield ancient potters may have gone in their seach
for suitable clay and temper within Manu'a.
TO'AGA TEMPER VARIANTS
The following variants ofbasaltic temper sand
are all pr in varying numbers of To'aga sherds,
and each is described in detail in subsequent passages:
(a) Profise Basaltic Temper: Seven sherds (1-5,
7, 14) contain ferromagnesian basaltic sand so
abundant that it forms 50-60 percent ofthe sherd
bodies. The proportions of grain ypes in six (1-5, 7)
of the sherds are statistically indiuis e, but
the seventh (14) contains a related volcanic sand of
slightly different composition.
(b) Sparse Basaltic Temper: Twelve sherds (6,
10, 13, 16, 19-23, 27-29) contain sparse feremnagnesian basaltic sand of somewhat different composition
and texture. The mineral and lithic grains form only
5-15 percent of the sherd bodies, but about a third
(25-40 percent) of the temper grains used may have
been fragments ofbroken pottery.
(c) Feldpathic Basaltic Temper: Three sherds
(15, 17, 18) contain feldspathic basaltic sand, which
152
The To'aga Site
fonns a normal prport (30-40 percen) of the
sherd bodies and is both mineralogically and texturt the two ferroma
ally disinc from
an variants of
Toaga tper. Another sherd (9) contins a similar
but sparser temper sa (A15
i percent of body) that
appears to be a hybrid sand with a significant
e of detritus from the kinds of bedrock
sources that yielded the feromagesia basaltic
sands.
(d) Mixed Temper Sand: Seven sherds (8, 11,
12, 24-26, 30) contain mixed teper sands composed of both basaltic and reefdetitus in varying
poportions. Fcrwmagnesian mineral grai and
basaltic litc fragmens do the volcanic sand
components of the mixed tempers, but their proportions are highly variable and plagioclase feldspar
grains are al pesent in some sherds.
temmed "slabwor') display blocky to prismatic
subhedral pyroxene crystals iergrown with aggregated and multiply twined plagioclase crystals of
slabmike aspect. Lithic fragments of intermediate
grain size (here termed "latiwotk) display disorented mosaics oftwinned plagioclase laths with
equant and largely anhedral pyroxene grains within
their interstices. As all gradations are seemingly
present between "slabworkW and 'lathwodc" and
'tachylitic" grains, the distinction made among hem
is useful in a qualitatve sense only. Groundmass
iron oxides in lithic fragmes range from equant or
granularto skelet or elongate in form without
apparent regard to other aspes of internal texture.
TEMPER GRAIN TYPES
The fenomagnesian volcanic sands in sherds
with profuse basaltic temper are moderately sorted
assemblages of subangular to subounded grains
with a texture suggestive of alluvial orgin. Unmistable rounding of the edges of many gains
indicates n rally occuming sand, rather than
artificially cnmshed aggregate, and local ravine
streams may have provided the sources of the
temper. As would be expected for such a setting,
lithic fragmens are generally but not uniformly
larger than mineral grains. Abundance of
subangular silty basalt detritus within the clayey
paste in which the temper sand is imbedded suggests
that potters collected naturally tempered sandy clay.
This circumstance may account for the superabundance of temper sand in proportions higher than
typically encountered in Pacific Island sherds.
Proportions of grain types in most sherds containing
this alluvial temper are quite consistent (table I0.1):
half pyroxene, a quarter lithic fragments, a fifth
olivine, and a trace of opaque iron oxides. All
micrhenocrysts in lithic fragments are pyroxene
and olivine. As the inteal texture of lithic fragments is somewhat variable, being ree-quarters
'lathwok" in two sherds (1, 7) and two-thirds
"slabwok" in four others (2, 5), collecting sites were
evidently closely related but not identical. Nevertheless, the average temper composition (table 10.1) for
the six sherds in which proportions of grain types are
essentially the same is taken here to be the best
estimate, petrlogically speaking, of proportions of
consituents for characteristic To'aga temper.
The non-calcareous components of all the
To'aga temper types are without exception composed
of mineral grains and lithic fragments derived
entirely from basaltic bedrock sources, eiter lavas
or pyroclastic deposits, together mi some cases with
fragments of broken pottery. The mineral grains,
originally phenocrysts or micrphenocrysts in basalt,
include clinopyroxene, olivine, opaque iron oxides
(magnetite anid/or ilmenite), and plagioclase feldspar.
The lithic fr s, represing aphanitic groundmass of basaltic lava or tephra, display a spectrum of
internal textures reflecting an inherent range of
constituent grain sizes. Microphanocrysts in lithic
fragments include all the mineral species that were
also p t in the temper sands as separate mineral
gams
Routine distinction between pyroxene and
olivine in thin section was based upon key diagnostic
features visible for each grin, and their identifications were checked by observations ofoptic axial
angle and birefringence on suitably oriented grains.
Pyroxene grains generally display faint green tints,
and many show either cleavage or prismatic shapes.
Untinted olivine grains are brighter in plane light,
and many are altered along edges and fIracues to
bright reddish iddingsite. Most basalt lithic fragments have an intergranuar internal texture, although the finest gained (here tenmed "tachylitic")
ae intersertal with plagioclase microlites set in black
basaltic glass (tachylite). The coarsest grained (here
PROFUSE BASALTIC TEMPER
Sand Temper in Prehistoric Potsherds
153
Table 10.1
Frequency Percentages of Ferromagnesian Mineral
Grains' and Basaltic Volcanic Lithic Fragments (VRF)
in Sherds Containing "Profuse Basaltic Temper"
Sherd
1
2
3
4
5
7
Ave
14
n
Py
01
Fe
VRF
Py(Py+01)
130
160
210
105
185
260
51
50
53
51
50
54
52
36
21
23
20
17
24
23
21
14
2
2
1
4
4
1
2
3
26
25
26
28
22
22
25
47
0.71
0.68
0.73
0.75
0.78
0.71
0.71
0.72
'Py, clinopyroxene; 01, olivine; Fe, opaque iron oxides
Note: n=number of grains counted in each sherd and average (Ave) composition is calculated for sherds
1-5 plus 7 but not 14.
A seventh sherd (14) contains distinctly more
lithic volcanic sand (table 10.1), although its pyroxene/olivine ratio is very close similar to that of the
other sherds. Lithic fragments, mostly "lathwork,"
are also more irregular in shape and some are
microvesicular. Curved re-entrants on some lithic
fragments and the presence of a few grains of
microvesicular brownish basaltic glass suggest a
pyroclastic component lacking in the more characteristic six sherds whose tempers were probably
derived entirely from bedrock lava sources.
SPARSE BASALTIC TEMPER
The ferromagnesian volcanic sands in sherds
with sparse basaltic temper are well sorted aggregates of subrounded grains with a texture suggestive
of beach origin. The lack of finer grained grit within
the clayey paste suggests that potters added artificial
temper to clay bodies. Dark angular blotches within
the clayey paste are probably ghosts of broken
pottery fragments also added as pain of the tempering
process. Although recognition of this grog constituent is equivocal in some sherds owing to indistinct
outlines of the pottery fragments, its presence may
account for the low overall proportion of volcanic
sand, which amounts alone to much sparser temper
than typically encountered in Pacific Island sherds.
Frequency percentages of grain types are highly
variable for different sherds (table 10.2), but so few
grains are present in each sherd (average of only 20
per sherd in 10 of the sherds) that the statistical
significance of individual counts is questionable.
Consequently, all grains (250 total) were summed
from all sherds counted to yield net frequency
percentages, but net and average temper compositions are almost identical (table 10.2). The fact that
both measures of bulk composition are similar to
values for the single sherd (22) containing the most
grains (60) gives confidence that either measure is a
valid estimate of the overall temper composition.
The sparse basaltic temper, probably beach sand, is
less pyroxenic and more lithic than the average
composition of the dominant alluvial variant of the
profuse basaltic temper, but grain proportions closely
resemble those in the more lithic variant of alluvial
sand. In general, differences are not great enough to
suggest wholly different provenance except for the
contrast between stream and beach collecting sites.
Proportons of lithic grain types are quite variable
from sherd to sherd, but all three types are present in
subequal amounts within the suite of twelve sherds
as a whole. The net pyroxene/olivine ratio (0.63) is
only slightly lower than in the alluvial sands (0.72),
and may have been reduced marginally by preferential cleaving of pyroxene grains and winnowing of
resulting cleavage fragments during prolonged
reworking in a beach environment.
154
The To'aga Site
Table 10.2
Frequency Percentages of Ferromagnesian Mineral Grains
and Basaltic Volcanic Lithic Fragments (VRF) in
Sherds Containing "Sparse Basaltic Temper"
Sherd
6
10
16
19
20
21
22
23
27
28
29
Net
Ave
n
Py
01
Fe
VRF
20
10
15
30
10
10
60
25
30
20
20
250'
5
40
47
33
30
40
42
32
40
25
25
34
33
10
20
33
13
20
20
20
20
40
5
15
20
20
5
10
7
4
10
10
2
8
3
5
5
4
6
80
20
13
50
40
30
36
40
17
55
55
42
41
'Summation of n for 11 sherds listed.
Note: n=number of grains counted in each sherd (note that net and average compositions
are essentially the same). Sherd 13 too weatherd to allow accurate count.
FELDSPATHIC BASALTIC TEMPER
The volcanic sand in sherds (15, 17, 18) containing feldspathic basaltic temper essentially lacks
fenrmagnesian mineral grains (table 10.3), and
nearly all microphenocrysts in lithic fragments are
plagioclase rather than pyroxene or olivine. One
olivine grain is present, however, in one sherd (18),
and one olivine microphenocryst is present in
another (15). Lithic fragments are consistently
larger than separate plagioclase mineral grains,
although the two are present in about the same
frequency (table 10.3), and the sand overall is only
moderately sorted. Most lithic fragments are
"tachylitic," many have smoothly curved re-entrants
typical of tephra clasts, and some are microvesicular.
The textural features of the sand jointly suggest that
scoiaceous basaltic as, possibly reworked locally,
was added as artificial temper to the clay body by
potters having some selective aim in using such a
tempering material The feldspathic basaltic temper
shows no compositional overlap with the fenomagnesian basaltic tempers, but the geograhic separa-
tion of their respective sources need not have been
great. As if to underscore that point, one sherd (9)
contains well-sorted and subrounded temper,
probably a beach sand, that apparently represents a
mixture of feldspathic and ferromagnesian volcanic
sands. This anomalous sherd has an apparently
sparse temper (- .15% of body) but also includes a
few fragments ofbroken pottery as part of its overall
temper component.
MIXED TEMPER SAND
The volcanic sands in sherds containing an
admixture of reef-derived calcareous grains (15-75
percent) are highly variable in mineralogical composition (table 10.4). Although all are dominantly
ferromagnesian volcanic sands, nearly half contain
feldspathic components as well. Coupled with the
presence of the calcareous grains, the good sorting
and rounding of the sands is diagnostic of coastal
origin on beaches where mixing of detritus from
multiple sources is to be expected. Proportions of
temper sand vary from 10-25 percent (8, 11, 12, 24)
155
Sand Temper in Prehistoric Potsherds
Table 10.3
Frequency Percentages of Plagioclase Feldspar (P1) and Opaque Iron Oxide
(Fe) Mineral Grains and Basaltic Volcanic Lithics Fragments (VRF) in
Sherds Containing "Feldspathic Basaltic Temper"
Sherd
15
17
18
Ave
9
n
P1
Fe
VRF
60
35
125
43
50
56
50
18
8
6
4
6
7
49
44
40
44
59
60
Py
01
-
-
-
-
-
-
-
-
13
3
Note: n=number of grains counted in each sherd and average (Ave) composition is calculated for sherds 15
plus 17-18 but not 9 (Py and 01 are clinopyroxene and olivine mineral grains in sherd 9).
Table 10.4
Frequency Percentages of Calcareous Grains (calc), Silicate-Oxide
Mineral Grains, and Lithic Fragments for Sherds Containing "Mixed
Temper Sand"
Sherd
8
11
12
24
25
26
30
Calc
n
Py
01
Fe
P1
VRF
13
22
20
15
44
18
77
65
35
12
30
70
160
60
32
14
33
27
21
22
39
32
7
17
23
17
18
14
3
7
25
-
-
1
1
2
1
5
20
33
72
25
50
60
54
25
Note: n=number of non-calcareous grains counted in each sherd (percentages reported sum to 100
exclusive of calcareous grains)
to 40-60 percent (25, 26, 30), the "tachylitic" variety
of lithic fragments form about half the lithic popula-
DISCUSSION: TEMPER COMPARISONS
mon, and the overall pyroxene/olivine ratio ('0.60) is
similar to that in the other sherds thought to contain
beach sand temper. Computation of an average or
net composition for the sherds containing mixed
sand temper would be meaningless, given their
inherent compositional variability, but their volcanic
sands fit broadly within the spectrum of temper types
present in other sherds. Sherds containing only
sparse mixed temper sand also contain fragments of
broken pottery in uncertain amounts.
Although each of the To'aga temper types has
clear distinguishing characteristics, compositional
links argue that they form a related temper suite that
is presumably indigenous to Manu'a. The two
ferromagnesian basaltic tempers have contrasting
textures tat reflect different sedimentological
origins such as stream and beach sands, but the same
grain types are present in both in slightly different
proportons. The admixture of similar fenomagnesian constituents in one ofthe sherds containing
156
The To'aga Site
feldspathic basaltic temper suggests hat bedrock
sources for the fenomagnesian and feldspathic
volcanic sands exist not far apart This inference is
strengtned by the observation that mixed beach
sands containing calcareous grains contain a varied
spectrum of fenomagnesian and feldspathic constituents.
Prehistoric sherds examined previously from
Upolu (Dickinson 1969,1974,1976) contain
generally similar basaltic temper sands composed of
the same basic grain types, but none of the 'Upolu
tempers is identical in texture or composition to the
To'aga tempers. Fenromagnesian basaltic tempers
from 'Upolu commonly contain a higher proportion
oflithic fragments, typically have a higher ratio of
olivine to pyroxene, and generally contain a subordinate proportion of brownish basaltic glass particles
not present in To'aga tempers. Moreover, Upolu
ferromagnesian tempers
sherds with a
contain well-sorted coastal sands texturally unlike
the stream sands evident in well tempered To'aga
sherds. Feldspathic basaltic tempers from 'Upolu are
broadly similar to their To'aga analogs, but internal
textures of lithic fragments differ in being coarser
gained in the lJpolu sherds studied to date. Feldspathic trachytic tempers present in all available
Upolu collections apparently have no counterparts at
To'aga.
The generic resemblance of all Samoan temper
types examined to date pennits the strong inference
that the tempers in To'aga sherds are indigenous to
Samoa. On balance, there is no reason to suppose
on petrographic evidence that any of the To'aga
temper types were derived from sites elsewhere in
Samoa. The fragments ofbroken pottery present in
about half the To'aga sherds are not common constituents ofPacific Island wares, but do occur in sherds
from the Ryukyu Islands, Palau, and the Nan Madol
site on Ponape (Dickinson and Shutler 1979; Dickinson et al. 1990). Their presence at To'aga presumably reflects a common paucity of suitable local
temper sand, rather than any close cultural relationship between the Caroline Islands region and Samoa.
REFERENCES CITED
Dickinson, W. R 1969. Temper sands in prehistoric
potsherds from Vailele and Falefa. IN R. C.
Green and J. M. Davidson, eds., Archaeology
in Western Samo, Vol. I: pp. 271-73,
Auckland Institute Museum Bulletin 6.
. 1974. Temper sands in shends from Mulifanua
and comparison with similar tempers at Vailele
and Sasoa'a (Falefa). IN R. C. Green and J. M.
Davidson, eds., Archaeology in Western
Samoa, Vol. II: pp. 179-80, Auckland Institute
Museum Bulletin 7.
1976. Mineralogy and petrology of sand
tempers in sherds from the Feriy Beth site,
Paradise site, and Jane's Camp. IN J. D.
Jennings, R N. Holmer, J. C. Janetski, and H.
L. Smith, eds., Excavatios on 'Upolu, Western
Samo, pp. 99-103. Pacific Anthrpological
Records 25. Honolulu: Bernice P. Bishop
Museum.
Dickinson, W. R, and R. Shutler, Jr. 1968. Insular
sand tempers of prehistoric pottery from the
southwest Pacific. IN I. Yawata and Y. H.
Sinoto, eds., Prehistoric Culture in Oceania,
pp. 29-37. Honolulu: Bishop Museum Press.
1971. Temper sands in prehistoric pottery of the
Pacific islands. Archaeology and Physical
Anthropology in Oceania 6:191-203.
-.1979. Petrography of sand tempers in Pacific
islands potsherds. Geological Society of
America Bulletin 90 (Part I, summary):993-95;
and Part II (microfiche), No. 1 1, Card 1, pp.
1644-1701.
Dickinson, W. R. J. Takayamna, E. A. Snow, and R.
Shuder, Jr. 1990. Sand temper of probable
Fijian origin in prehistoric potsherds from
Tuvalu. Antiquity 64:307-312.